(1) Field of the Invention
The present invention relates to a cap with valve, such as a fuel cap or a radiator cap for automobiles, which is installed to an aperture of a container such as a fuel tank or a radiater and adjusts pressure in the container.
(2) Description of the Prior Art
Such a cap with valve in the prior art, for example, a fuel cap to be installed to a filler neck of an automobile is disclosed in Japanese utility model application laid-open No. 179654/1985 (U.S. Pat. No. 4,572,396) as shown in FIGS. 1-2.
In a fuel cap 1, an annular seal member 3 is provided with lip elements 3a, 3b projecting downwards at outer and inner peripheries respectively, and an annular groove 3e is formed on upper surface of the inner lip element 3b so that the inner lip element 3b is positioned lower than the outer lip element 3a. The annular groove 3e of the seal member 3 is fitted to a stepped porion 4b of an annular support plate 4 thereby the seal member 3 is assembled and held to the support plate 4. At inside of a cap body 2 threadedly installed to a filler neck 10, the outer lip element 3a of the seal member 3 is pressed against a stepped portion 2b of a fluid flow path 2a of the cap body 2 through a bias means, and the inner lip element 3b is pressed against a valve plate 5 through a bias means. A spring shoe 6 is provided at the center with a fluid flowing hole 6a, and arranged on upper side of the fluid flow path 2a. A coil spring 7 as a bias means urges the support plate 4 downwards, and presses the outer lip element 3a of the seal member 3 against the stepped portion 2b. Also a coil spring 8 presses the valve plate 5 against the inner lip element 3b from a spring shoe 3c extending downward from the stepped portion 2b. An upper cover 9 is fitted to upper side of the cap body 2.
At rear side of the outer and inner lip elements 3a, 3b in the seal member 3, recesses 3c, 3d to make each radial length constant are formed throughout the whole circumference at rear side of the outer and inner lip elements 3a, 3b so that prescribed gap h is provided between the seal member 3 and the support plate 4 at non-pressed state of the seal member 3.
Operation state of the fuel cap 1 will be described. First, when pressure in a fuel tank (not shown) is positive, the valve plate 5, the seal member 3 and the support plate 4 are elevated against the biasing force of the spring 7. Since the outer lip element 3a of the seal member 3 and the stepped portion 2b of the cap body 2 are separated from each other, fluid such as air in the tank flows from the fluid flowing hole 2d of the spring shoe 2c through the gap and the fluid flowing hole 6a of the spring shoe plate 6 so as to adjust the pressure within the tank. On the contrary, when the pressure in the fuel tank is negative, the valve plate 5 is lowered against the biasing force of the spring 8. Since the inner lip elements 3b of the seal member 3 and the valve body 5 are separated from each other, fluid such as air flows from the fluid flowing hole 6a of the spring shoe 6 and the fluid flowing hole 4a of the support plate 4 through the gap and the fluid flowing hole 2d of the spring shoe 2c into the tank so as to adjust the pressure within the tank.
In the fuel cap 1, prescribed recesses 3c, 3d are formed on rear side of the outer and inner lip elements 3a, 3b of the seal member 3 so that gap h is formed between the seal member 3 and the support plate 4 at non-pressed state of the seal member 3. Consequently, even if surface precision is slightly low at the outer and inner lip elements 3a, 3b and the stepped portion 2b and the valve plate 5 to constitute seal portions thereof or the support plate 4, the error can be absorbed by the gap h between the outer and inner lip elements 3a, 3b and the support plate 4.
When the seal member 3 is held to the support plate 4, since the annular groove 3e is formed on upper side of the seal member 3 near inner periphery thereof and the assembling holding is possible by only fitting the annular groove 3e to the stepped portion 4b of the support plate 4, the support plate 4 and the seal member 3 can be easily assembled.
In the fuel cap 1, the recesses 3c, 3d are formed at rear side of the outer and inner lip elements 3a, 3b of the seal member 3 so as to absorb the error in surface precision of each member. Consequently, when the outer and inner lip elements 3a, 3b are pressed against the stepped portion 2b and the valve plate 5 being seal portions thereof through the coil springs 7, 8, the outer and inner lip elements 3a, 3b are bent respectively about contact positions X, Y as fulcrum of the seal member 3 in the recesses 3c, 3d with the support plate 4 at bottom portion in radial direction.
It is preferable for seal performance or valve opening sensitivity of the seal member 3 that distance between the outer and inner lip elements 3a, 3b and fulcrums X, Y thereof becomes equal throughout the whole circumference and biasing force by the coil springs 7, 8 is transmitted uniformly to the outer and inner lip elements 3a, 3b throughout the whole circumference.
In the fuel cap 1, however, the seal member 3 is fitted and assembled through the stepped portion 4b of the support plate 4. Moreover, the seal member 3 is usually made of elastomer and therefore resilient. Consequently, the outer and inner lip elements 3a, 3b of the seal member 3 are liable to become eccentric with respect to the support plate 4 during assembling, and care must be taken well in the assembling work. If care is not taken, distance between the outer and inner lip elements 3a, 3b and bottom portions of the recesses 3c, 3d as bending fulcrums X, Y thereof will not become uniform throughout the whole circumference. Since the biasing force by the coil spring 7, 8 is not uniformly transmitted to the outer and inner lip elements 3a, 3b throughout the whole surface, the seal performance of valve opening sensitivity is affected.
Consequently, the fuel cap 1 mut be improved in the assembling property of the seal member 3 to the support plate 4 and in securing the constant distance of the lip elements to the bending fulcrums throughout the whole circumference to affect the seal performance or valve opening sensitivity.